<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style type="text/css">
.box {
    display: flex;
    background-color: white;
}
.box-item {
    width: 200px;
    height: 200px;
    line-height: 200px;
    vertical-align: middle;
    margin: 5px;
    background-color: #ffd200;
    font-size: 100px;
    color: white;
    text-align: center;
}
.box-item div {
    font-size: 14px;
    position: relative;
    top: -150px;
}
.grow {
    flex-grow: 1;
}
.grow-2 {
    flex-grow: 2;
}
    </style>
</head>
<div class="box">
    <div class="box-item grow">1<div>(flex-grow: 1)</div></div>
    <div class="box-item">2<div>(width: 200px)</div></div>
    <div class="box-item grow">3<div>(flex-grow: 1)</div></div>
</div>
</body>
</html>